Merge pull request #8620 from takluyver/i8618

Fix suppression of exception chaining with 'raise ... from None'

IPython/core/tests/test_ultratb.py

@@ -173,6 +173,13 b' except Exception as e:'
     raise KeyError('uh')
     """
 
+    SUPPRESS_CHAINING_CODE = """
+try:
+    1/0
+except Exception:
+    raise ValueError("Yikes") from None
+    """
+
     def test_direct_cause_error(self):
         if PY3:
             with tt.AssertPrints(["KeyError", "NameError", "direct cause"]):
@@ -182,3 +189,9 b' except Exception as e:'
         if PY3:
             with tt.AssertPrints(["KeyError", "NameError", "During handling"]):
                 ip.run_cell(self.EXCEPTION_DURING_HANDLING_CODE)
+
+    def test_suppress_exception_chaining(self):
+        if PY3:
+            with tt.AssertNotPrints("ZeroDivisionError"), \
+                    tt.AssertPrints("ValueError", suppress=False):
+                ip.run_cell(self.SUPPRESS_CHAINING_CODE)

IPython/core/ultratb.py

@@ -985,6 +985,8 b' class VerboseTB(TBTools):'
             cause = getattr(exception_value, '__cause__', None)
             if cause:
                 return cause
+            if getattr(exception_value, '__suppress_context__', False):
+                return None
             return getattr(exception_value, '__context__', None)
 
         chained_evalue = get_chained_exception(evalue)